Actually, the eruption only blew a mile off the mountain, and the rest collapsed into the empty magma chamber.
Also, it's the deepest lake in the United States (1,943 ft) and the 7th deepest in the world.
(By the way, I read that Anthony Watts denies the existence of Crater Lake,
as well as most of southern Oregon, except, oddly, those areas
of the coastal region that are both less than 10 miles from the
shoreline and greater than 10 feet in elevation.)